Multi-layer container and preform and process for obtaining same

ABSTRACT

A multi-layer preform, includes: (a) a plastic inner liner, comprised of a cylindrical walled body, which may or may not include a tapered annular shoulder portion, and a cylindrical walled neck portion extending upwardly from the body, and (b) a molded outer layer. Prior to the outer layer being molded over the plastic inner liner, at least a portion of the liner is crystallized by a heat treatment process. The molded outer layer may include a means to receive a closure device. When the preform is at an acceptable temperature range for orientation, the multi-layer preform can be blow-molded to form a multi-layer container having improved properties.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. patent application Ser. No.09/203,302, filed Dec. 1, 1998, still pending, which is aContinuation-In-Part of copending U.S. patent application Ser. No.08/861,477, filed May 22, 1997, now abandoned, by William A. Slat.

TECHNICAL FIELD

This invention is directed toward containers and container preforms, andmore particularly to multi-layer containers and preforms having improvedphysical properties.

BACKGROUND ART

In recent years, plastics have become widely used in the field ofcontainers for food products, beverages, cosmetics, and for numerousother applications. Polyester resins, such as polyethylene terephthalate(“PET”), have become very popular because they can be blow molded intothin-walled containers having excellent physical properties andcharacteristics.

Conventional blow molding of plastic containers typically involves twosteps. In the first step or phase, an intermediate article, or preform,is formed. The second phase involves biaxially orienting the preforminto the final article by a process commonly referred to as blowmolding, or stretch blow molding. Many of the properties of the plasticmaterial are best realized once the container has been biaxiallyoriented and blow molded. Quite commonly during such processing, theneck portion of the preform is used as a mounting portion for theblowing mold and the finish or threaded area of the preform is notspecifically heated. Also, because that segment of the preform is notfully oriented, it will not exhibit the full benefit of propertiesresulting from the biaxial blow molding method. For instance, PETcontainers in which the neck region has not been subjected to, or morefully subjected to, an orientation often exhibit reduced thermalresistance to deformation.

While the previously mentioned two-step process is frequently used toproduce large volumes of containers for a variety of applications, in anumber of specialized applications, the product content must be filledat elevated temperatures to ensure proper sterilization. For instance,beverages which are pasteurized, such as some European drinks, arebottled in a range of 148° to 170° F. Drinks which include a portion offruit juice are typically hot-filled in a range of 170°-185° F.Moreover, some fruit drinks and the like, require even higher hot-filltemperatures, i.e., 190° to 200° F. and above, to achieve an appropriatelevel of purification.

Elevated filling temperatures pose a challenge in constructing plasticcontainers because thermoplastic materials are known to increase inplasticity with temperature over time. Exposure of the container to thecontents at higher fill temperatures can cause portions of the articleto soften and deform, making it more difficult to maintain thecontainer's structural integrity. This is especially true when longerperiods of time are involved and/or when the temperature of the hot-fillproduct exceeds the glass transition temperature of the plastic, i.e.,the temperature at which plastic changes from a solid to a soft, rubberystate. For reference, the glass transition (“T_(g)”) or softeningtemperature of PET is approximately 170° F.

When the filling temperature approaches or exceeds transitiontemperature of the polymer, container manufacturers often employadditional thermal conditioning techniques to help avoid the associatedthermal shrinkage and resulting distortion. In a number of applications,it becomes necessary to stiffen specific portions of the container toprevent an unacceptable amount of deformation. This is especially truefor the neck region when hot-filling product contents at about 185° to200° F. or higher, or when causing a closure roll-on die or a luggedneck finish to apply a closure means to the final container.

In the case of PET containers, non-discriminate heat treating of theentire container would induce spherulitic crystal growth innon-molecularly oriented portions of the container. The resultingcontainer would have opaque, brittle portions, and would be commerciallyundesirable. As such, controlling the crystallization process is a basicconsideration in determining the physical properties of the container.

The prior art discloses the practice of incorporating a heat treatmentprocess to stiffen the neck section of preforms and/or containers.Essentially, heat treatment is used to induce crystallization at theneck portion of the preform or container in an effort to increasethermal resistance to deformation. The primary drawback with suchmethods is that it generally takes a significant amount of time tosufficiently heat treat the thickness of the neck portion, it being oneof the thickest portions of the preform. Because this process can becostly and time-consuming, there exists a need to develop techniques forimproving the properties of the upper, or neck, portion of preforms andthe resultant containers in a more commercially efficient manner.

In addition to heat treating processes, manufacturers of plasticcontainers often attempt to take advantage of the use of multiple layersof plastic materials. Such multi-layer containers, i.e., those havingmultiple layers throughout all or portions of the article, often proveto be more desirable than their mono-layer counterparts for a number ofhot-fill applications. This is often because the individual layers of amulti-layer structure may provide independent benefits and the layerscan be selected from materials to better optimize functionalcharacteristics. Multi-layer containers have found an increasing role inthe manufacture of plastic containers and are commonly known to thoseskilled in the art.

Therefore, by employing processes which take advantage of both themulti-layered structure along with limited and controlledcrystallization, one skilled in the art can best adapt the physicalstructure of the container to meet the needs of a given application.

DISCLOSURE OF INVENTION

Accordingly, an object of this invention is to provide a multi-layerpreform and container made therefrom and process for obtaining same inwhich the neck portion is partially crystallized to enhance themechanical strength and thermal resistance of the article.

Another object of the present invention is to provide a multi-layerpreform and container made therefrom and process as aforesaid in whichthe neck portion of the preform has an at least partially crystallizedliner which provides sufficient hardness and is produced in a morecommercially efficient manner, especially with a relatively thin liner.

A further object of the present invention is to provide a multi-layerpreform and container made therefrom and process as aforesaid withreduced deterioration in the physical properties of the neck portion andwherein the resultant container is better suited for specializedapplications.

Still another object of the present invention is to provide amulti-layer preform and container made therefrom and process asaforesaid wherein the resultant container can withstand filling athigher temperatures without excessive deformation and may better receivea closure device.

The present invention provides a multi-layered plastic preform formanufacturing a blow molded container, comprising a plastic inner linerhaving a thickness from 0.010-0.030 mils and having a cylindrical walledlower portion and a cylindrical walled upper portion integral with andextending upwardly from said lower portion, wherein at least a portionof said upper portion of the plastic inner liner is crystallized by aheat treatment process; and an injection molded outer layer that iscontinuous with substantially the entire length of the plastic innerliner, wherein said preform has a closed bottom and an open neck andwherein the inner liner is crystallized separately from and prior toinjection molding of the outer layer.

The present invention also provides a container blow molded from amulti-layered preform, comprising: a plastic inner liner having athickness from 0.010-0.030 mils and having a cylindrical walled lowerportion and a cylindrical walled upper portion integral with andextending upwardly from said lower portion, wherein at least a portionof said upper portion of the plastic inner liner is crystallized by aheat treatment process; and an injection molded outer layer that iscontinuous with substantially the entire length of the plastic innerliner, wherein said preform has a closed bottom and an open neck andwherein the inner liner is crystallized separately from and prior toinjection molding of the outer layer.

In addition to the foregoing, the present invention also provides aprocess which comprises: preparing a plastic inner liner having athickness from 0.010-0.030 mils and having a cylindrical walled lowerportion and a cylindrical walled upper portion integral with andextending upwardly from said lower portion; crystallizing at least aportion of the upper portion of the plastic inner liner by a heattreatment process; and forming a preform by injection molding an outerlayer over the plastic inner layer subsequent to crystallization of theupper portion of the liner, with the outer layer being contiguous withsubstantially the entire length of the inner liner and with said preformhaving a closed bottom and open neck. The process also includes the stepof blow molding the preform to form a blow molded container.

The objects, features and advantages of the present invention arereadily apparent to those skilled in the art from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the following drawings wherein like referencecharacters depict like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational sectional view of a mono-layer plastic liner.

FIG. 2 is an elevational sectional view of another embodiment of amono-layered plastic liner which is more generally suited for containershaving wider mouth openings.

FIG. 3 is an elevational sectional view of a multi-layer plastic liner.

FIG. 4 is an elevational sectional view of another embodiment of amulti-layered plastic liner which includes a tapered walled shoulder anda defined upper portion.

FIG. 5 is a cross-sectional view of the top end of a preform liner beingsubjected to a heat treatment process.

FIG. 6 is a view of one possible method for heating and handling liners.

FIG. 7 is an elevational sectional view of a preform in which a portionof the liner has been subjected to a heat treatment process and an outerlayer, including a threaded portion, has been molded over the liner.

FIG. 8 is an elevational view showing the process of blow molding thepreform into the container.

FIG. 9 is an elevational view of one type of container made inaccordance with the principles of the present invention.

FIG. 10 is an elevational view of another type of container having awider mouth opening which is made in accordance with the principles ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings in detail, wherein like reference numeralsand letter designate like elements, there is shown in FIG. 1 anelevational view of a single- or mono-layer liner, also referred to as apreform sleeve, designated generally as 10. The liner 10 furtherincludes an upper portion 12 and a lower portion 14, the lengths ofwhich can each be adjusted to meet the needs of a given application. Theupper portion 12 of the liner 10 is desirably thin, ranging from0.010-0.30 mils, since this portion will be separately crystallized andmore rapid crystallization can be obtained with a thin upper portion.For most applications, the length of the upper portion 12 should beapproximately the length of the threaded portion of the preform whichwhile eventually be used to form the desired finished article. The liner10 itself can be formed from any number of polyester materials, such asPET, polyethylene napthalate (PEN), ethyl vinyl alcohol (EVOH) and/orvarious blends of the same. However, in the majority of cases,particularly those in which the finished article will hold contents fitfor human consumption, the liner 10 will be formed from virgin PET orsome other FDA-approved resin.

The liner 10 may be formed by an extrusion process, such as thatdisclosed in U.S. Pat. No. 5,464,106, by a thermoforming process, suchas that taught by U.S. Pat. No. 5,443,766, by an injection moldingprocess, by a compression molding process, or any other conventionalprocess. However, for most containers extrusion is the preferredprocessing technique for forming a thin-walled liner 10 having acontrolled wall thickness along its length.

In FIG. 2, another embodiment of a mono-layer liner is shown. In thatfigure, the wide-mouth liner 10 a has a larger mouth or opening diameterrelative to the diameter of the finished article than the samecomparative measurements of the liner 10 of FIG. 1. However, thewide-mouth liner 10 a is preferably formed by thermoforming, injectionor compression processes, rather than by an extrusion process.

Referring now to FIG. 3, a multi-layered liner 10 b is shown which iscomprised of an inner layer 30 and an outer layer 40. When producingcontainers designed to hold contents for human consumption, the innerlayer 30 is comprised of a polyester material which is acceptable forsuch a purpose. The outer layer generally will not contact the contentsand generally can be comprised of less expensive polyester resins. Inpractice, the multi-layered liner 10 b is not limited to just an innerand outer layer and can consist of any number of multiple layers takenalong cross sections of all or a portion of its length. Because it isoften desirable to form a thin inner or barrier layer, the liner 10 bwill preferably be formed by an extrusion or co-extrusion process.However, injection molding, compression molding, or other processesknown in the art can be employed in various combinations to produce asimilar multi-layered structure.

Another embodiment of a multi-layered liner 10 c is shown in FIG. 4. Themulti-layered liner 10 c in the drawing includes multiple layers havinga lower closed portion 50, a side wall portion 52, a tapered cylindricalwall-shaped shoulder portion 54, and an upper portion 56 located abovethe shoulder portion 54. As long as the liner 10 c can be properlytransported and handled on core pins or other handling means, theprecise shape and taper of the shoulder portion 54 is not critical.

The properties of polymers are dramatically affected and primarilydetermined by molecular structure. In general, polymers are classifiedas either crystalline (actually semi-crystalline) or amorphous. Theordered, three-dimensional arrangement of molecules results incrystallinity. It is important to note that polymers invariably containa proportion of amorphous material, i.e., that which is “without form”and lacking an internal skeleton or structure. As such, polymers havevarying degrees of crystallinity.

Percent crystallinity of a polyester material can be given by thefollowing formula:

% CRYSTALLINITY=(d _(s) −d _(a)) /d _(c) −d _(a))×100,

where,

d_(s)=density of the test sample in g/cm³;

d_(a)=density of an amorphous film in zero percent

crystallinity (for PET, 1.333 g/cm³; and

d_(c)=density of the crystal calculated from unit cell

parameters (for PET, 1.455 g/cm³).

Density measurements for the foregoing formula are made by the densitygradient method described by given standards, more particularly ASTM1.505.

The amount of percent of crystallinity has a significant effect upon theproperties of a given polyester material. Also an increased degree ofcrystallinity raises the melting point, increases density, and generallyimproves mechanical properties. The crystallization of bulk polymers,such as PET, is characterized by the formation of large crystallineaggregates, or spherulites. However, increased crystallinity alsogenerally lowers impact strength, solubility, and optical clarity.Because the molecular chains are only partly ordered, most crystallineplastics are not transparent in the solid state. Such crystallinestructures within the polymers act to scatter light and givepolyethylene and polypropylene a milky appearance. In contrast, polymersare transparent if most crystallinity can be prevented.

The amount of crystallinity achievable in a heat treated article is afunction primarily of the heat treatment. By strategically controllingand directing the amount of crystallization at various portions of aplastic article, the physical characteristics can be better tailored toa given function. Depending upon the material employed and the desiredcrystallinity, heat treatment temperatures may range from the upper endof the orientation temperature range to in excess of 450° F. (232.2°C.). As the intrinsic viscosity of the polyester increases, thetemperature needed to achieve a given percent crystallinity will alsoincrease. Because of the foregoing factors, the heat treatment times fora given liner 10 can vary from a second or two to several minutes. Thethin liner of the present invention enables more rapid heat treatmenttimes while still obtaining significantly improved properties.

To impart controlled crystallization, some time after the liners 10(such as those shown in FIGS. 1-4) are formed, a means for heating andcrystallizing at least a portion of the liners 10 is employed. Thecrystallization of the specified portions of the liner 10 may beeffected by heating in an oven with a thermal source or heat-generatorsuch as an infrared heater or block of heaters, by utilizing radiofrequency heating techniques, or by any other process known to those inthe art. For reference, the crystallinity of the specified heat treatedupper portion 12 of a PET liner 10 will be preferably between 5 and 50%,and more preferably between 20 and 45%.

FIG. 5 shows one form of heating means 60 being used to crystallize aportion of the upper portion 12 of a generally straight-walled,mono-layered liner 10. In the embodiment exemplified in FIG. 5, a heater72 comprising an electromagnetic inductor is provided in a frame wall(not shown) in such a manner that radiant heat is concentrated on justthe desired upper portion 12 of the liner 10. As shown in greater detailin FIG. 6, this operation can be accomplished while the liners 10 arebeing transported to a subsequent station and are being rotated past oneor more banks of heaters 72. In the embodiment exemplified in FIG. 5,the liners 10 will be transported by rows in recesses 74, or “pockets”,which cover the lower portion 14 of the liners and leave the desiredupper portion 12 of the liners 10 exposed for heat treatment andcrystallization as the liners are rotated at a constant speed andtransported past one or more heaters 72 which may be located on one orboth sides of the liner transporting system 76, as clearly shown in FIG.6.

The heating temperatures for the upper portion 12 of the liners 10 willgenerally be predetermined or adjustably programmed or controlled on thebasis of the thickness, contour and the like of the liner 10 beingconditioned, with the thin liners of the present invention facilitatingrapid processing. Additionally, by spinning or revolving the liners 10past the heaters 72, a more uniform heat distribution can be imparted onthe desired portion of the liner 10. If heated at a sufficienttemperature for a sufficient duration of time, the desired portion ofthe liner 10 will become crystallized and may take on a milky whiteopaque appearance. Naturally, any of the liners in FIGS. 1-4 may be sotreated.

Because the upper portion 12 of the liner 10 may undergo thermalshrinkage deformation from the heat treatment, for some applications,additional techniques may be employed to reduce the amount of thermaldeformation and better maintain dimensional stability. For example, onesuch method involves the insertion of a die pin (not shown), or similarholding device, into the open portion of the upper portion 12 of theliner to prevent inward deformation during heat treatment. The die pinor other holding device may preferably have a cylindrical shape slightlysmaller than the bore of the open upper portion 12 of the liner 10 priorto heat treatment, as well as a tapered tip to facilitate its removalfrom the liner 10.

However, the invention is not limited to the heating and handling meansdescribed above, and any conventional means to impart or direct asufficient amount of heat to the desired portion of the liner 10, may beemployed to specifically crystallize and thermally treat the desiredsegment of the liner 10. Because the walls of the liner 10 being heattreated are much less thick that the walls of the preform, as little asone-fifth the thickness or less, the heat treatment process willcorrespondingly take much less time than it would to treat a thickerpreform, thereby resulting in processing efficiencies. Furthermore, theheat-treated liners 10 can be formed and stored until needed for furtherprocessing.

Reference is next made to FIG. 7. After the desired portions of theliner 10, or any of the liners in FIGS. 1-4, have been sufficiently heattreated and crystallized, an outer layer 80 of a thermoplastic polyesteris molded around the liner 10 to form a multi-layered preform 90. In thepreform 90 shown in FIG. 7, the crystallized segment of the liner 10 isdesignated by the number 84. While various molding processes, includingcompression molding, may be used to form the outer layer 80, thepreferred method is injection molding. The crystallized liner 10 isplaced in the cavity of a conventional injection mold and the outerlayer 80 is subsequently injection molded around the liner 10 as shownin FIG. 7 to form the preform 90. Additionally, for most applicationsthe outer layer 80 of the preform 90 includes a means for securing aclosure device. Most commonly, threads 86 are injection molded into theneck finish of the outer layer 80 of the preform 90 and are designed toaccept a screw-type cap. Although it is not viewed as a requirement, forcertain applications, the upper dispensing end 88 of the preform 90 canadditionally be subjected to a secondary heat treatment or heat-settingprocess to stiffen the outer molded layer adjacent the inner plasticliner. Such secondary heat treatment can be accomplished by any ofseveral conventional techniques for stiffening the neck of a preformwhich are well-known in the art. Thus, as shown in FIG. 7, outer layer80 includes closed bottom, body portion 94 extending upwardly therefromand threaded neck portion 96 extending upwardly from body portion 94.The body portion of the outer layer and the cylindrical walled lowerportion of the liner in combination have a thickness from 0.110-0.170mil, preferably from 0.145-0.150 mil.

With the configuration taught by this invention, a multilayered preform90 can be formed to incorporate advantages associated with differentlayers and materials having varied levels of crystallization alongdifferent portions of their vertical lengths. For instance, the upperportion 12 of the liner 10, such as that corresponding and adjacent tothe relatively unoriented portion of the molded outer layer 80, can beheat treated as desired to impart a given range of crystallinity therebyproviding certain inherent characteristics, such as increased thermalstability and improved mechanical properties. Surprisingly, despite thethin liner, the improved properties in the upper liner provides greatlyimproved properties in the preform and resultant container with rapidprocessing. At the same time, the corresponding portion of the moldedouter layer 80 of the preform 90, which is not directly heat treated toinduce or increase crystallization, will provide other desirablephysical characteristics such as higher strength and better opticalclarity.

Once the multi-layer preform 90 has been formed and is brought to anappropriate temperature profile, if necessary by re-heating, the preform90 can then be placed into a blow mold 100, shown in FIG. 8. In the blowmold 100, the preform 90 is held securely by an engagement of the moldwith at least a portion of the upper dispensing end 88 of the preform90. Once proper placement is established, the blow molder 102 is used toblow the preform 90 into the final shape of the container. The portionof the preform 90 secured by the mold, including the correspondingportions of the plastic inner liner 10 which have been heat treated andthe molded outer layer 80, will not experience the full biaxialorientation imparted by the blow molding process. Hence, such sectionsof the respective layers will have slightly different physicalcharacteristics than the portions of the same layers which were securedduring the blow molding process.

For a PET container 110, the density of the non-secured, biaxiallyoriented (strain crystallized only) transparent region will be generallybelow 1.36 grams/cc, whereas the density of the thermal and straincrystallized finish region will be substantially above 1.37 grams/cc.Thus, for example, the oriented, transparent regions will have acrystallinity below 22% while the crystallized regions will have acrystallinity above 30%.

After the preform 90 is formed into the container, the blow mold 100 isopened and the completed container 110 is removed. FIGS. 9 and 10 showtwo styles of containers, respectively designated 110 a and 110 b, whichcan be produced utilizing the principles of the instant invention.However, an unlimited number of designs can be contemplated.

Although the above description contains many specific references todetailed information, such specificity should not be construed aslimiting the scope of the invention, but as merely providing anillustration of some of the presently preferred embodiments of theinvention. Obviously, numerous modifications and variations of thepresent invention are possible in light of the above teachings. It istherefore understood that the invention may be practiced other than asspecifically described herein and the scope of the invention should bedetermined by the appended claims and their legal equivalents, ratherthan by the examples given.

What is claimed is:
 1. The process which comprises: preparing a plasticinner liner having a thickness from 0.010-0.030 mils and having acylindrical walled lower body portion and a cylindrical walled upperportion integral with and extending upwardly from said lower portion;crystallizing at least a portion of the upper portion of the plasticinner liner by a heat treatment process while protecting the lowerportion of the liner from the heat treatment process; and forming apreform by injection molding an outer layer over the plastic inner layersubsequently to crystallization of the upper portion of the liner, withthe outer layer being contiguous with substantially the entire length ofthe inner liner and with said preform having a closed bottom and openneck.
 2. The process of claim 1, including the step of blow molding saidpreform to form a blow molded container.
 3. The process of claim 1,wherein the inner liner is prepared by one of extruding andthermoforming.
 4. The process of claim 1, wherein the outer layer isinjection molded to provide said outer layer with a closed bottom, abody portion extending upwardly therefrom and a threaded neck portionextending upwardly therefrom, wherein the body portion and cylindricalwalled lower body portion of the liner in combination have a thicknessfrom 0.110-0.170 mil.
 5. The process of claim 1, wherein the upperportion of the liner has an outer surface area, and including heattreating said liner upper portion to provide greater than 20% of theouter surface area in a crystallized state.
 6. The process of claim 1,including the step of preparing a multi-layered inner liner.
 7. Theprocess of claim 6, including preparing said multi-layered liner with atleast one layer of a plastic barrier material.
 8. The process of claim7, including preparing said multi-layered liner with said barrierselected from the group consisting of ethylene vinyl alcohol (EVOH),polyethylene naphthalate.
 9. The process of claim 1, including heattreating at least a portion of the outer layer.
 10. The process of claim1, including the step of heat treating the upper portion of the linerwhile protecting the lower portion of the liner from heat treatment. 11.The process of claim 1, including forming said outer layer with a closedbottom, a body portion extending upwardly therefrom, and a neck portionextending upwardly therefrom, wherein the lower portion of the innerliner is adjacent the body portion of the outer layer and the neckportion of the outer layer is adjacent the upper portion of the innerliner.